Electrolyte solution and electrochemical device

Abstract

An electrolyte solution intended for use in electrochemical devices which can achieve a high capacitance retention ratio even after long-term use at high voltage. The electrolyte solution of the present invention includes a mononitrile compound (I), at least one compound (II) selected from dinitrile compounds and trinitrile compounds, and a quaternary ammonium salt (III). The amount of the compound (II) in the electrolyte solution is 0.05 to 5% by mass.

The invention claimed is: 
     
       1. An electrolyte solution comprising
 a mononitrile compound (I), 
 at least one compound (II) selected from the group consisting of dinitrile compounds and trinitrile compounds, and 
 a quaternary ammonium salt (III), 
 the amount of the compound (II) being 0.05 to 5% by mass in the electrolyte solution, 
 wherein the dinitrile compound is a compound represented by the following formula (II-a):
   NC—R 2 —CN  (II-a)
 
 
 
       wherein R 2  represents a C1-C8 alkylene group which may have a fluorine atom,
 wherein the mononitrile compound (I) is at least one selected from the group consisting of acetonitrile and propionitrile. 
 
     
     
       2. The electrolyte solution according to  claim 1 ,
 wherein the trinitrile compound is a compound represented by the following formula (II-b):
   NC—R 3 —CX 1 (CN)—R 4 —CN  (II-b)
 
 
 
       wherein X 1  represents a hydrogen atom or a fluorine atom, and R 3  and R 4  may be the same as or different from each other and individually represent a C1-C5 alkylene group having a fluorine atom. 
     
     
       3. The electrolyte solution according to  claim 1 ,
 wherein the quaternary ammonium salt is a tetraalkyl quaternary ammonium salt or a spirobipyrrolidinium salt. 
 
     
     
       4. The electrolyte solution according to  claim 1 ,
 wherein the quaternary ammonium salt is a spirobipyrrolidinium salt. 
 
     
     
       5. The electrolyte solution according to  claim 1 ,
 wherein the amount of the quaternary ammonium salt is 0.1 to 2.5 mol/L. 
 
     
     
       6. The electrolyte solution according to  claim 1 ,
 which is intended for use in electrochemical devices. 
 
     
     
       7. The electrolyte solution according to  claim 1 ,
 which is intended for use in electric double-layer capacitors. 
 
     
     
       8. An electrochemical device comprising
 the electrolyte solution according to  claim 1 , a positive electrode, and a negative electrode. 
 
     
     
       9. The electrochemical device according to  claim 8 ,
 which is an electric double-layer capacitor. 
 
     
     
       10. The electrochemical device according to  claim 9 ,
 wherein the electric double-layer capacitor comprises a polarizable electrode which contains activated carbon formed of a carbonized coconut shell.